A nonvolatile charge trapping memory is demonstrated on a thin film transistor (TFT) using a solution processed ultra-thin (~7 nm) zinc tin oxide (ZTO) semiconductor layer with an Al2O3/Ni-nanocrystals (NCs)/SiO2 dielectric stack. A positive threshold voltage (V
TH) shift of 7 V is achieved at gate programming voltage of 40 V for 1 s but the state will not be erased by applying negative gate voltage. However, the programmed V
TH shift can be expediently erased by applying a gate voltage of −10 V in conjunction with visible light illumination for 1 s. It is found that the sub-threshold swing (SS) deteriorates slightly under light illumination, indicating that photo-ionized oxygen vacancies (
Carrier transport properties of solution processed ultra thin (4 nm) zinc-tin oxide (ZTO) thin film transistor are investigated based on its transfer characteristics measured at the temperature ranging from 310 K to 77 K. As temperature decreases, the transfer curves show a parellel shift toward more postive voltages. The conduction mechanism of ultra-thin ZTO film and its connection to the density of band tail states have been substantiated by two approaches, including fitting logarithm drain current (log ID) to T−1/3 at 310 K to 77 K according to the two-dimensional Mott variable range hopping theory and the extraction of density of localized tail states through the energy distribution of trapped carrier density. The linear dependency of log ID vs. T−1/3 indicates that the dominant carrier transport mechanism in ZTO is the variable range hopping. The extracted value of density of tail states at the conduction band minimum is 4.75 × 1020 cm−3 eV−1 through the energy distribution of trapped carrier density. The high density of localized tail states in the ultra thin ZTO film is the key factor leading to the room-temperature hopping transport of carriers among localized tail states.
In this study, a charge trapping thin-film transistor (TFT) is demonstrated based on a zinc−tin oxide (ZTO) semiconductor channel layer and a stack of AlO x /AZO nanoparticles/SiO 2 as the gate dielectrics. This device can be switched from the pristine state to the charge trapping state via the application of a positive gate voltage pulse (V G = 40 V for 1 s). When the TFT is set at the charge trapping state, the dynamic photoresponse (to light in the wavelength of 405 or 635 nm) of drain current gain can be significantly enhanced as compared to that of the device set at the pristine state. As a comparison, the ZTO TFT without the nanoparticulate AZO layer exhibits neither charge trapping nor enhanced photoresponse characteristics. The enhancement in the dynamic photoresponse of the charge trapping TFT is attributed to the increasing number of electrons at the ZTO channel by lightassisted detrapping charges. The methodology used in this study provides a unique approach to achieve photosensitive and photostable duality within a single device.
Charge-trapping memories (CTMs) based on zinc tin oxide (ZTO) semiconductor thin-film transistors (TFTs) can be programmed by a positive gate voltage and erased by a negative gate voltage in conjunction with light illumination. To understand the mechanism involved, the sub-gap density of states associated with ionized oxygen vacancies in the ZTO active layer is extracted from optical response capacitance–voltage (C–V) measurements. The corresponding energy states of ionized oxygen vacancies are observed below the conduction band minimum at approximately 0.5–1.0 eV. From a comparison of the fitted oxygen vacancy concentration in the CTM-TFT after the light-bias erasing operation, it is found that the pristine-erased device contains more oxygen vacancies than the program-erased device because the trapped electrons in the programmed device are pulled into the active layer and neutralized by the oxygen vacancies that are present there.
This study addresses the variation in gate-leakage current due to the Fowler-Nordheim (FN) tunneling of electrons through a SiO2 dielectric layer in zinc-tin oxide (ZTO) thin film transistors. It is shown that the gate-leakage current is not related to the absolute area of the ZTO active layer, but it is reduced by reducing the ZTO/SiO2 area ratio. The ZTO/SiO2 area ratio modulates the ZTO-SiO2 interface dipole strength as well as the ZTO-SiO2 conduction band offset and subsequently affects the FN tunneling current through the SiO2 layer, which provides a route that modifies the gate-leakage current.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.